1. Field of the Invention
The present invention relates to a spring member for an acceleration sensor, to the acceleration sensor using the spring member, and to a magnetic disk drive apparatus with the acceleration sensor.
2. Description of the Related Art
In a magnetic disk drive apparatus or a hard disk drive (HDD) apparatus assembled in a mobile equipment such as for example a walkabout personal computer, a mobile phone, a digital audio player and other mobile gear, an HDD apparatus used as a mobile storage itself or a removable HDD apparatus, in order to prevent a collision of a magnetic head with a hard disk surface due to drop impact, it is necessary to detect the instant at which the HDD apparatus falls before occurrence of the drop impact and to retract the magnetic head from the hard disk surface. Such instant of the falling can be detected from a slight change in the acceleration of gravity.
U.S. Pat. No. 6,131,457 (Japanese patent publication No. 11-352134A) discloses an acceleration sensor for detecting a small change in the acceleration of gravity. This acceleration sensor has a magnetic body including a mass point on an axis along a Z-axis, mounted to a vibrator having three-dimensional freedom, and four or more magnetoresistive effect (MR) detector elements positioned on an X-axis and a Y-axis with their centers located along a perimeter of a concentric circle around the origin point of the orthogonal coordinate axes. The sensor is thus capable of detecting each of acceleration in the direction of X-axis through a relative difference in output voltage between the two detector elements on the X-axis due to a vibration of the magnetic field, acceleration in the direction of Y-axis through a relative difference in output voltage between the two detector elements on the Y-axis due to a vibration of the magnetic field, and acceleration in the direction of the Z-axis through a sum total of the output voltages of all the detector elements.
However, because this known acceleration sensor disclosed in U.S. Pat. No. 6,131,457 is configured to detect the Z-axis acceleration by summing the output voltages of the detector elements for the X-axis acceleration and the Y-axis acceleration, it is quite difficult to increase detection sensitivity in the Z-axis acceleration. Thus, in order to detect the Z-axis acceleration with high sensitivity, it is necessary to add an acceleration-detection mechanism specifically designed for detecting the Z-axis direction acceleration.
As for the acceleration-detection mechanism specifically designed for detecting the Z-axis direction acceleration, Japanese patent publication No. 06-201723A discloses an acceleration sensor with an elastic magnetic metal body attached to a housing in a cantilever manner so that this magnetic metal body and the housing are capable of relatively moving, and a strain resistance element mounted on the magnetic metal body. However, because the acceleration sensor described in Japanese patent publication No. 06-201723A is configured to detect the strain of the magnetic metal body and to utilize the strain resistance effect of the strain resistance element, it is difficult to expect a high sensitive detection of the Z-axis acceleration. Also, because it is necessary to have electrodes for extracting detection signals on the magnetic metal body itself, the structure of the sensor becomes complicated due to the lead lines connected to the electrodes. Furthermore, when the magnetic metal body is miniaturized, wiring process of such lead lines becomes extremely difficult. Also, the lead lines formed on the miniaturized magnetic metal body may induce breakage of the lead lines when an excessive value of impact is applied, and prevent distortion of the magnetic metal body to interface with the improvement in sensitivity of the sensor. This tendency becomes more pronounced as the acceleration sensor becomes smaller.
In addition, combination of such acceleration sensor specifically designed for detecting the Z-axis direction acceleration with the acceleration sensor for detecting the X-axis acceleration and the Y-axis acceleration makes miniaturization of the acceleration sensor more difficult.